Published online by Cambridge University Press: 11 May 2009
The free living eulimid gastropod Melanella alba Bowdich, 1822 is a temporary ectoparasite on echinoderms and, in Kilkerrin Bay on the west coast of Ireland, this species is found exclusively associated with the holothuroid Neopentadactyla mixta (Östergren), 1898. Melanella utilizes a highly specialized acrembolic proboscis to penetrate the integument and ingest the internal tissues of this holothuroid. That portion of the proboscis which penetrates integument bears a highly developed secretory epithelium composed of granular and goblet secretory cells. As the proboscis is unfolded into the host's integument by a combination of increased hydrostatic pressure and muscular movements, secretory material is released from this epithelium and appears to bring about a rapid loosening of the connective tissue elements of the host. The possible mechanism by which the integumental connective tissue is altered to allow unfolding of the proboscis into the coelomic cavity of the host is discussed.